1. Field of the Invention
The present invention relates to a printing machine, and more particularly, to an automatic sheet feeder of a printing machine having a maximized sheet feeding efficiency and durability by minimizing the frictional load during the feeding operation thus by preventing the occurrence of stepping out and abrasion of respective components or paper double feeding and slippage.
2. Description of the Prior Art
Generally, an automatic sheet feeder (ASF) is an essential part of a printing machine which picks up each sheet of paper and conveys the picked sheet of paper to a printing section.
FIGS. 1 and 2 show one example of such an automatic sheet feeder.
Conventionally, the so-called "compensator type ASF" has been used in which gears 1 driven by a driving motor (not shown) drive a rotational shaft 2, to rotate a compensator 3 disposed on the rotational shaft 2 toward a paper loading section 4. Being rotated toward the paper loading section 4, the compensator 3 comes into contact with the first sheet of paper P loaded in the paper loading section 4, and picks up and feeds the first sheet of paper P through a paper feeding roller 5 which is mounted on an end of the compensator 3 and rotated by the driving force transmitted from the rotational shaft 2.
Here, paper pick up devices in almost all kinds of automatic sheet feeders (inclusive of the above-described automatic sheet feeder) pick up and feed a sheet of paper P by the rotational force of the paper feeding roller 5 in a state that the paper feeding roller 5 is pressed into contact with a paper friction pad 6 which is made of cork material and attached on the bottom of the paper loading section 4.
Since the conventional automatic sheet feeder 10 does not have any means for detecting the presence of the paper P in the paper loading section 4, many problems have been caused by the printing operation started by the printing command in the absence of the paper P in the paper loading section 4.
More specifically, when the printing operation is carried out in the absence of paper P, due to the frictional force generated between the rotating paper friction pad 6 and the paper feeding roller 5, noise is produced between the rotating paper friction pad 6 and the paper feeding roller 5, and finally, faulty sheet feeding operation of the printing machine such as paper double feeding or slippage occurs as the paper feeding roller 5 and the paper friction pad 6, which are capped by a rubber material, are quickly worn out.
Further, the overload caused by the frictional force between the paper feeding roller 5 and the paper friction pad 6 may also cause stepping out of the components such as the motor and gears 1, etc., damaging the printing machine.
The above-mentioned problems shorten the life span of the printing machine, deteriorating the reliability which results in user dissatisfaction.